Spinal rods are used for spinal fixation operations, often times for correction of scoliotic curves. Fixation using such rods often involves the use of plates and/or screws for retaining the rods and operative connection with the spine. Usually, a pair of rods are placed on opposite sides of the portion of the spine to be fixed. Various systems, usually transverse connectors, have been developed for cross linking spinal rods to prevent rod migration and to increase stiffness of the paired rod assembly. Such connectors are used in corrective operations where the rod is rotated to correct spinal curvature. The transverse connectors can be use to further stabilize the rod to rod positions.
Many assemblies used for interconnecting spinal rods, referred to as transverse connecting assemblies or rod to rod couplers, utilize a plate mechanism having connectors for adjustably retaining hook systems that are bolted in place in the plate. Examples of such systems are U.S. Pat. No. 5,334,203 to Wagner, issued Aug. 2, 1994, and U.S. Pat. No. 5,522,816 to Dinello, et al. issued Jun. 4, 1996. The U.S. Pat. No. 5,498,263 to Dinello, et al. issued Mar. 12, 1996, discloses a transverse connector system utilizing set screws to interconnect vertebrae coupling members while using plate members as described above for interconnecting the coupling members such that a squared unit is formed having two sides defined by the plate member and two sides defined by the spaced rod members.
U.S. Pat. No. 5,312,405 to Korotko, et al. issued May 17, 1995 discloses a coupler used for interconnecting spinal rods where the coupler itself is a two piece unit, the neck portion of each unit being interconnected by a screw mechanism which clamps a male portion within a female portion of the system. This system also utilizes couple inserts or yokes which engage a rod. The rod is disposed within a seat portion of each coupler and compressed by an instrument which engages the bottom of the rod between the rod and the spine and the top of the coupler. U.S. Pat. No. 5,275,600 to Allard, issued Jan. 4, 1994, discloses a telescoping rod to rod coupler wherein the connector bodies are interconnected by a telescoping mechanism which varies the distance between the coupled bodies. A telescoping connection is also disclosed in the U.S. Pat. No. 6,328,741 to Richelsoph, issued Dec. 11, 2001.
The U.S. Pat. Nos. 6,171,311 and 6,328,740, both to Richelsoph, issued Dec. 11, 2001, and Jan. 9, 2001, respectively, each disclose a transverse connector including a pair of transverse connector bodies and connector inserts for connecting a rod to each of the transverse connector bodies. Both patents disclose inserts including threaded neck portions for being connected by a connector through an opening in the base portion of the connector bodies. A locking and fixing mechanism draws the inserts into seat portions of the transverse connector bodies while simultaneously locking the transverse connector inserts in the insert seat portions and compressing the rods seat surface of the insert to lock a rod within the seats. More specifically, a neck member engages and locks the insert within an insert seat. In order to affect the locking mechanism, the surgeon must use a threaded nut to engage threads on the insert member to draw it into the connector body and lock the assembly on the spinal rod.
It would be desirable to be able to securely hold and lock an insert, retaining a rod therein, in the locked position without threads, nuts, set screws, or other hardware. Further, it is desirable to provide a mechanism for sharing loads between the connector body portions without increasing the height of the profile of the insert while controlling rigidity and allowing load sharing.